It is a mystery

One of the things that can help is to stand with just your toes on the edge of a stair and let your ankles sink as low as they'll go below the level of your toes, hold it for a bit, and then rise as high as you can on tiptoes, hold that, and repeat a few times.

Important to have something to hold and good traction for your toes! Plus the usual "don't bounce" and "slowly" caveats.

One of the tricky bits with anything whole-body is that the ow usually winds up wherever the muscles have to manage the strain, but that isn't necessarily where the muscles are weakest; that can be where the compensating behaviour goes. So it can be effective to work the bits that aren't aching some.